Field of the invention
The present invention relates to a microwave dielectric ceramic composition. More particularly, the present invention relates to an economically favorable microwave dielectric ceramic composition superior in long-term reliability, such as high-temperature resistance and humidity resistance.
Description of the Prior Art
U.S. Pat. Nos. 5,219,809 and 5,164,882 suggest dielectric compositions, both similar in main composition and sintering aid, which are useful materials for components of, e.g. communication equipment, disclosing that the applicapability and productivity of the components are generally improved as their dielectric constants decrease and the sintering temperatures decrease.
Kato et al. reported in Jpn. J. Appl. Phsy. 30(9B) 2343(1991) and 32(9B) 4356(1993) a dielectric ceramic composition with high dielectric constant, consisting mainly of lead oxide (PbO), calcium oxide (CaO) and zirconium oxide (ZrO.sub.2), which was developed by an oxide combining technique. According to J. Am. Ceram. Soc., 74[6] 1320-1324 (1991) of Shinitchihirano et al., Zr(0.8)Sn(0.2)TiO(4) composition has a dielectric constant of about 40, a quality factor of over 5,000 and a temperature coefficient of resonant frequency of below 20 ppm/.degree. C. However, this composition is difficult to prepare as it requires pulverization to fine particles of 0.3 .mu.m through alkoxide technique and high temperature sintering of about 1,600.degree. C. but shows a relative low dielectric constant.
The above microwave dielectric ceramic compositions show dielectric constant and quality factor enough to be used as a material for dielectric resonators, but because the sintered dielectric material is not of fine structure, if the dielectric resonators are used for a long time at a high temperature and humidity region, they become poor in quality factor and unstable in the temperature coefficient of resonant frequency and thus, the filter characteristic is lowered.